Mostly people who were understandably pissed off that along with wiping out his blogs, twitter, etc., he took down his github and abandoned his projects without helping to oversee a transition of stewardship. This included a few high-profile rubyists.
And then presumably also some people who always thought his whimsy was a detriment to the ruby community (by making it seem less professional or something).
There's a difference between talented programming and good engineering, and _why is almost a perfect example of that. Engineering is more about discipline and maintainability than cleverness and artistic expression.